In many internal combustion engines, the engine crankshaft typically drives a balance shaft assembly to reduce engine vibration and noise due to the mass forces associated with the cyclic accelerations of reciprocating pistons and their connecting rods. Balance shafts are required to maintain substantially fixed angular timing relationships with the engine's crankshaft in order to fulfill their force cancellation functionality. And while single balance shafts are sometimes used for such purposes, many engines utilize two balance shafts. Regardless of whether a single balance shaft or multiple balance shafts are utilized, proper and adequate lubrication of the balance shaft bearings is essential in light of the shafts' rotational speed rates and associated centrifugal loadings.
Oil provides lubrication for the balance shaft bearings, as well as the other components of the engine. An oil pump may be driven by, or connected to, one of the balance shafts, the engine's crankshaft, or other drive mechanisms. During operation of the engine, the oil pump operates to provide pressurized oil to the various components of the engine by means of a network of pressurized oil passages. To ensure that clean oil is sent through the system, the oil is typically forced through an oil filter by the oil pump to remove contamination, debris, wear residue, and other foreign substances.
The network of pressurized oil passages within an engine's lubrication system typically extends to include the bearings of its balance shafts when present. If any contamination is resident in the oil passages between the oil filter and the balance shaft bearings when the engine is initially assembled, it will not be filtered out of the oil before reaching the bearings. Such build-phase contamination risks damage to balance shaft bearings, especially hydrostatic-type bearings at the extremities of current art lubrication passage networks where the oil passages terminate, leaving only bearing-to-journal running clearance as escape route for the oil and its possible contaminants to return back to the sump. If the oil contains contaminants larger than can readily escape the very small oil film clearance gap, they will be trapped at the lubrication network terminal bearings, where cyclic motion of the shaft's journal can work them into the clearance gap and produce bearing damage. Damage to balance shaft bearings can lead to engine failure, especially if oil pump functionality is impaired or lost.
Therefore, there exists a significant need for a balance shaft bearing lubrication system capable of readily and efficiently flushing debris and other such contaminants from the balance shaft bearings in order to desensitize the engine system to the risk of failure due to build-phase contamination of its lubrication circuit.